Chargeable portable devices are in widespread usage. For example, many people bring a chargeable cellular phone with them most if not all of the time. Most portable chargeable devices include a display that indicates the charge state of the device so that the device can be charged prior to the device becoming completely discharged.
When traveling in a motor vehicle, chargeable devices can be charged via a vehicle charger power adapter. Many vehicle charger power adapters include an input connector configured to connect to a vehicle 12 volt power outlet and a voltage converter that converts the 12 volt direct current power to generate 5 Volt direct current power used to charge the device. When the vehicle motor is running, the vehicle battery is kept charged via power produced by the vehicle alternator.
When the vehicle motor is stopped, however, power output via the vehicle 12 volt power outlet discharges the vehicle battery. If the power drained from the vehicle battery is sufficiently large, the vehicle battery may become discharged to a level that is insufficient to start the vehicle motor. To avoid such a situation, the vehicle may be intermittently run just to charge the vehicle battery, thereby consuming fuel and generating emissions.